This invention relates to drip irrigation, and, more particularly, to a drip-irrigation hose with an improved emitter construction, and like.
Drip irrigation systems are designed to deliver small amounts of water at selected locations along a hose. The hose carries water under pressure and the delivery of small amounts of water is achieved by discharging the water through small orifices, or emitters, with high hydrodynamic resistance to the flow of water.
Two types of drip hoses have contributed to the world-wide diffusion of drip irrigation: tapes and tubing. Tapes are collapsible hoses with thin walls in the range 4-20 thousandth of an inch, operating at low pressure, typically in the range of 5-20 psig, with built-in orifices. They are made from a strip of plastic film, upon which molten plastic beds for the orifices are deposited, and the sides of the strip bent over each other and welded to form a multi-chamber hose. Tubing has thicker, more rigid, walls than tapes and the most popular types of tubing have pre-installed emitters. The tubing is manufactured by extrusion and the emitters are simultaneously inserted in succession within the tube as the tube is being extruded. Tapes are most commonly used for annual or seasonal row crop while tubing is used more often on perennial crop.
The emitters may be materially separate from the tube and inserted into the tube at longitudinally spaced locations, as shown in U.S. Pat. No 4,850,531, or may be integral to the tape construction and positioned near one another longitudinally along the tape to functionally approximate a Continuous line-source of water. In the case of emitters separate from the tube, the hydrodynamic resistance is generated by a small tortuous flow-path located within the emitter body, while in the case of tile integral emitters the hydrodynamic resistance to water flow is provided mainly by a long secondary flow-path of small cross-sectional area. as shown in U.S. Pat. No 4,247,051, with additional resistance coming from orifices of small cross-sectional area in communication with the secondary flow-path and in communication with the exterior of the hose, as shown in U.S. Pat. No 5,634,595.
Generally, when hydrodynamic resistance is produced by either a tortuous flow-path, or a secondary flow-path having an essentially fixed and non-deformable shape, the emitted water flow-rate increases significantly with internal hose pressure. This is an undesired property since hose pressure necessarily drops along the run of the hose due to friction (viscosity) to water flow, leading to the problem of over-watering plants at locations near the inlet of the hose, where the hose pressure is high, and under-watering plants distant from this inlet end, where the hose pressure is low. The uneven water delivery is aggravated when the hose is inclined with respect to the horizontal, as when lying on a hill, whereby the effect of gravity further increases the pressure variation along the hose.
In addition to the problem of uniform water ejection along the length of the irrigation hose, drip irrigation systems are prone to clogging from suspended particulates in the irrigation fluid. The supply of irrigation water must be filtered upstream of the irrigation hose to alleviate the clogging problem.
Recent developments in drip irrigation have shown that it is often advantageous to bury the irrigation hose below the ground to bring water directly to the root-system of the plants and avoid water-loss due to evaporation to the atmosphere, to reduce top-soil humidity leading to a reduction of grow of weeds and fungi and the corresponding reduction in the use of weed killers and fungicides, and to eliminate damages to the irrigation system caused by pickers, pruners and farm equipment.
Unfortunately, the clogging problem becomes particularly grave when the drip irrigation line is buried. The general experience so far accumulated with sub-soil irrigation has identified the following major problems:
intrusion of the tree root into the system through the orifices;
orifice and emitter clogging due to clay and silt entering the irrigation hose during de-pressurization of the hose at shut-down, (in addition to the conventional clogging caused by foreign particles carried by the irrigation water);
difficulty in detecting, locating, and repairing underground clogged orifices and emitters.
U.S. Pat. No. 5,785,785 etc, attempts to solve the problem of clogging and simultaneously achieve uniform water distribution along the run of the hose by using a secondary flow-passage with variable resistance, and flaps on the orifices that should keep environmental water from entering the hose when the hose is un-pressurized. However, upon close examination it is evident that the thinness of the wall material, quoted as being between 4 and 20 mils, does not supply enough rigidity to the orifices nor sufficient facial contact area between opposing walls of the orifice to seal the orifice when fluid pressure is removed from the hose.
U.S. Pat. Nos. 3,917,169 (1975), 3,970,251 (1976), 3,993,248 (1976), 4,077,570 (1978), 4,077,571 (1978), and 4,132,364 (1979), all by R. C. Harmony, attempt to solve the clogging problem and simultaneously achieve uniform water distribution along the run of the hose by using flexible skirts descending into the irrigation hose from the perimeter of each orifice, the skirts forming a channel leading to the discharge orifice. To generate a high hydrodynamic resistance in the channel, stria, or corrugations, are build into the surface of the skirts. The stria are claimed to generate turbulent and random flow that establishes a fluid pressure gradient along the channel. The combination of stria and flexible skirts is claimed to achieve a pressure-compensating function that provides a uniform distribution of water discharge along the length of the hose. For the stria to create the necessary pressure gradient, the skirts must be long and penetrate deep within the irrigation hose or tube. Consequently, the designs in the above mentioned patents by Harmony are incompatible with the established production techniques of tube extrusion or of tape rolling, folding and bonding. Furthermore, in all of Harmony""s designs the channel leading to the orifice has a convergent shape, being widest at the entrance and narrowest at the orifice. This convergence is conducive to clogging from within when particles are present in the irrigation fluid.
Accordingly, several objects and advantages of our invention are:
a) A pressure-compensated discharge emitter having a variable hydrodynamic resistance that increases with increasing pressure-drop across the emitter to produce a discharge flow-rate weakly dependent on the pressure-drop across the emitter;
b) An irrigation hose with a plurality of said pressure compensated emitters leading to an essentially uniform distribution of discharged irrigation fluid per unit time along the length of the hose, even in the presence of pressure variations along the hose;
c) A pressure-compensated discharge emitter providing a good self-closure when the hose is depressurized, thereby hindering soil and plant root ingestion into the emitter;
d) A pressure-compensated discharge emitter having low stress concentrations in the material surrounding the emitter.
e) A pressure compensated emitter buildable simultaneously with the irrigation tube during the extrusion process, without insertion of additional parts during the extrusion process.
f) A pressure compensated emitter for drip-irrigation tape, the emitter eliminating the need of secondary fluid conduits within the tape.
The present invention provides a drip irrigation system comprising: (a) a hose with a flexible wall circumscribing and bounding a main flow-path for carrying irrigation fluid, and (b) pressure-compensated emitters spaced along the length of the hose and providing a communicating channel between the main flow-path and a region at lower pressure outside the main flow-path, such as the region outside the hose, wherein the pressure-compensating function of the emitters produces a flow-rate through the emitters that is weakly dependent on the pressure differential across the emitters.
At least portion of the hose""s flexible wall is a single wall that directly separates the main flow-path from the region at lower pressure outside the main flow-path. The pressure compensated emitters are located on the single wall, and comprise
(a) one slit extending through the single wall, the slit interrupting the circumferential stresses in the single wall when the flow-path is pressurized, the stress interruption simultaneously causing a dilatation of the slit and an outwardly radial displacement in the single wall material adjacent to, and around the slit, and
(b) protrusions connected to the single wall and extending from the perimeter of the slit towards the main flow-path to form a discharge channel with an inlet facing the inward fluid region, the discharge channel connecting the inward fluid region to the slit, the protrusions narrowing the cross-sectional area of the inlet to increase the hydrodynamic resistance of the discharge channel in response to both the dilatation of the slit and to the outward displacement of the wall material adjacent to and around the slit.
The narrowing of the inlet increases the hydrodynamic resistance of the emitter in response to an increase in slit dilatation and outward displacement following an increase in pressure differential between the main flow-path pressure and the pressure in the outward receiving region, whereby the increase in hydrodynamic resistance counteracts the increase in pressure force to produce a discharge flow-rate weakly dependent on the pressure in the irrigation hose.
The use of protrusions responsive to the material deformation around the slit to create a narrow inlet that produces essentially all the hydrodynamic resistance, allows the protrusions to have a small height and be, therefore, easily incorporated in existing construction methods for tubes and tapes.
These and other features of the invention will be better understood through a study of the following detailed description of an embodiment of the invention when taken with the figures of the drawings. The scope of the invention, however, is limited only through the scope of the claims appended hereto.